This invention is related to the method of making heat resistant polyester in which the amount of the end carboxyl group is reduced.
It is well known that, in order to improve the thermal stability, i.e., the resistance to hydrolysis and resistance to aminolysis of polyester, the effective means is to reduce the amount of the end carboxyl group (hereinafter this will be referred to as (COOH)). Many methods of reducing the (COOH) of polyester have been proposed. Among them, however, the method of reacting with epoxy compound (Kokai Patent Publication No. 6051-1979 and many others) is known as the typical example. This prior method indeed reduces (COOH) but it also reduces the degree of polymerization.